The Fine-Structure of the Net-Circular Polarization in a Sunspot Penumbra

Abstract

We present novel evidence for a fine structure observed in the net-circular polarization (NCP) of a sunspot penumbra based on spectropolarimetric measurements utilizing the Zeeman sensitive FeI 630.2 nm line. For the first time we detect a filamentary organized fine structure of the NCP on spatial scales that are similar to the inhomogeneities found in the penumbral flow field. We also observe an additional property of the visible NCP, a zero-crossing of the NCP in the outer parts of the center-side penumbra, which has not been recognized before. In order to interprete the observations we solve the radiative transfer equations for polarized light in a model penumbra with embedded magnetic flux tubes. We demonstrate that the observed zero-crossing of the NCP can be explained by an increased magnetic field strength inside magnetic flux tubes in the outer penumbra combined with a decreased magnetic field strength in the background field. Our results strongly support the concept of the uncombed penumbra.

References in corpus (3)

• A dynamical model for the penumbral fine structure and the Evershed effect in sunspots
• Flux tubes as the origin of Net Circular Polarization in Sunspot Penumbrae
• The multi-component field topology of sunspot penumbrae - A diagnostic tool for spectropolarimetric measurements

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• 3D numerical MHD modeling of sunspots with radiation transport
• Filter Design for the Detection/Estimation of the Modulus of a Vector. Application to Polarization Data